Update Debian metadata and switch to default CI workflow

Requires Go from stretch-backports.
4 jobs for master in 1 minute and 57 seconds
Status Job ID Name Coverage
  Build Pkgsrc
passed #6933
build_pkgsrc:stretch

00:00:16

 
  Build Pkg
passed #6934
amd64
build_pkg:stretch:amd64

00:00:49

passed #6935
arm64
build_pkg:stretch:arm64

00:01:19

 
  Upload Pkg
passed #6936
upload_pkg

00:00:21